Switchable light modulating device

ABSTRACT

A controllable light reflective device made up of a chamber having at least a portion of its walls transparent to form a window therein with a light reflective structure forming part of or associated with said window. A fluid is placed in the chamber with structure for controllably displacing the fluid to and from a selected portion of the chamber and in optical cooperation with the reflective structure so as to control the amount of incident light which is reflected by the device through the window.

--'-- :ferencesCited UNITED STATES PATENTS 3,200,525 8/1965 Francis40/1-30 Primary Examiner- Ronald L. Wibert Assistant Examiner- Paul K.Godwin, .lr. Attorney-Frederick M. Arbuckle ABSTRACT: A controllablelight reflective device made up of a chamber having at least a portionof its walls transparent to form a window therein with a lightreflective structure fonning part of or associated with said window. Afluid is placed in the chamber with structure for controllablydisplacing the fluid to and from a selected portion of the chamber andin optical cooperation with the reflective structure so as to controlthe amount of incident light which is reflected by the device throughthe window.

PATENTED HAR30 |97I SHEET 1 [IF 2 INVENTOR. S/DA/EY .852 7-2pmSWI'ICHABLE LIGHT MODULA'I'ING DEVICE BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to light modulators and,more particularly, to a novel light ray reflector device wherein themagnitude of reflected light can be readily affected by externally andremotely applied switching stimuli.

2. Description of the Prior Art There have been many diverse attemptsdirected toward the solution of the problem of effective presentation ofdata provided as an output from a digital computer. The computer iscapable of performing high speed operations of a very complex naturethat are not directly meaningful to a human ob server. However, thefinal result of the computer data processing must, in many cases, bematched to the physiological, emotional, and intellectual capabilitiesof the human decision maker. This is particularly true of the commandand control environment associated with most of the present and plannedmilitary and space systems control center operations.

Although an initial consideration of the display problem may indicate atrivial solution, a detailed examination of the requirement demonstratesthe high order of complexity associated with the various parameters. Asa single example, the problem of pictorially providing a high-quality,updated map in full color in quasireal time (within one second from theinitiation of a request) on a large viewing screen of wall type withadequate resolution, brightness and accuracy are beyond the presentstate of the art. Modern display systems utilizing most or all of thefollowing technologies have been described: cathode ray tubes,transistor circuits, mechanics and electromechanics, opticalarrangements in the visible, infrared, and ultraviolet regions, filmexposure with wet and dry processing, heat flow, digital interface,human factors, fluid dynamics, and solid state physics.

In the display field today, many different techniques in use or in theprocess of development have the same system objective. In general,computer consoles are dependent upon cathode ray tube techniques andgroup displays, such as is represented by large viewing screens, or uponprojection optics. A typical system may, however, require the use ofboth wherein the console serves as an individual input-output device toinstruct or request operations on the part of the computer and whereinthe large viewing display provides the results of these and otherrequests for programs to a group audience. The significant techniquesthat have been used or are available for computer-console-driven groupdisplay systems can be placed into the following categories: (1.) filmgeneration and projection systems; (2.) electromechanically drivensystems; (3.) projection cathode ray tube systems; (4.) Schlierenprojection systems; (5.) electrostatic systems; (6.) photochromaticsystems; and (7.) electroluminescent materials.

None of these display systems satisfies the total requirement. Forexample, there are no major large screen computer oriented systemsincorporating film generation and projection systems that utilize a wetprocessing method. The reasons for this have been the high heatabsorption in the film gate, the necessity for drying the film prior toprojection, and the lack of stability of the film base material. The useof electromechanical elements in the display generation cycle of asystem implies that a tradeoff has been effected between the slowerresponse characteristics of the moving elements and the freedom of filmhandling and processing. In addition, the use of accurate discreteelements theoretically provides the possibility of very high accuracyand location of track data, although this has proved difficult to meetin practice.

With regard to Schlieren display systems, the problems with the use ofthis equipment are associated with the passage of the film in and out ofa vacuum chamber, the cooling of the film in the vacuum chamber, and thescratching of the film surface during transport. In electrostaticdisplay systems, the associated problems are temperature sensitivity,toner contamination, storage and retrieval. The display must either beprojecteddirectly from the toner dusted plate or be transferred to afilm or paper base with attendant ion of response time and resolution.Although photochromatic systems are characterized by high resolutionerasure and rewrite capacity; with no attendant processing, thedisadvantages are the necessity of high light intensity for exposure andthe wear of the photochromatic materials after about 1,000 reversals.

In regard to electroluminescence (EL) materials, the EL material orphosphor emits visible radiation from the excitation of an electricfield outside of a vacuum environment. The EL light display output isproduced by sandwiching a thin film of EL material between twoconductors, one of which must be transparent. The film in this elementalconfiguration is a few mils thick and requires excitation in the orderof 200-800 volts. The light display output increases approximatelyproportionately to the square of the voltage difference and the squareroot of the frequency difference. These characteristics, however, areinterrelated and vary with different phosphor combinations. The usualfrequency range is in the 400 to 5,000 I-lz range, and the drivingvoltages are limited by breakdown potential considerations and frequencyby the capacitance of the film structure as well as leakage excitation.The key problem area for the application of the EL material to a displaysystem is in the storage and switching of the information. Alphanumericor track data are provided through the selective actuation of segmentedportions of a 14 element matrix for each symbol. 2,000 symbols would,therefore,

require 28,000 bit switching. A large wall display with vector as wellas alphanumerics would require about 25 bits per inch for effectiveresolution. This, in turn indicates a total storage and switchingproblem in the 6,000,000 bit range. The addition of color changecapability requiring selection of other EL phosphor granules increasesthe problem complexity.

SUMMARY OF THE INVENTION The difficulties and problems encountered withvisual display systems as enumerated above are obviated by the lightmodulating device of the present invention, which provides for aswitchable light reflector cell that may be used to replace the panellights presently being used to indicate the ON/OFF state or condition ofvarious devices. Alternatively. any switchable light reflectors of theinvention can be assembled into a mosaic wherein the individualreflector devices may be controlled by a suitable pattern or displaygenerator so that the composite picture formed by the ensemble conveysdesired information to the human observer. Therefore, the device of thepresent invention can be employed as an individual display unit toindicate a condition or state, and,

when a plurality of devices are employed, a large wall-type viewingscreen or display surface may be provided wherein the pictorialinformation is generated by a digital process. Therefore, the presentinvention is adapted for use in a wide variety of display applications.and, since the light output from the controllable reflector device isderived from outside the device, it is particularly attractive for usein high light level environments that might render other types ofdisplays useless.

One form of the present invention is primarily based on a commonly knownand well understood phenomenonmamely, that of the reflection of light inpassing from a medium of high index of refraction to a medium of lowerindex of refraction. If the angle of incidence at the boundary orinterface exceeds the "critical angle," total reflection" occurs. If,however, the indices of refraction are nearly equal on the two sides ofthe interface, or in some instances where the light is made to pass froma first medium of relatively low index of refraction to a medium ofrelatively high index of refraction, incident light will be largelytransmitted into the second medium andonly a very small percentagereflected.

In general, the light modulating device embodying this form of thepresent invention provides a first light transparent medium having agiven index of refraction and a second medium having a lower index ofrefraction than the first medium. A third medium having an index ofrefraction substantially equal to or greater than the first medium isprovided, and means are included for controllably moving the second andthird media immediately adjacent the first medium so as to cause lightincident from the first medium to either be substantially totallyreflected away from the second medium or be transmitted into the thirdmedium.

In a more specific form of the invention, an enclosure is providedincluding a prism structure formed at one end thereof having a displaysurface adapted to be viewed by an observer with one or morewedge-configured rear surface protrusions projecting into the chamberdefined by the enclosure. A displacer element is disposed in saidenclosure chamber having a forward surface disposed in substantiallyfixed spaced-apart relationship so that a chamber space is definedimmediately behind the prism and in front of the displacer elementforward surface. The enclosure is suitably dimensioned to accommodatevertical movement of the displacer element with restriction of lateralmovement effected by the provision of guides on the displacer elementcooperating with the inner wall surfaces of the enclosure chamber. Thechamber is filled in part with a fluid medium having an index ofrefraction substantially equal to or greater than the refractive indexof the material composing the prism. When the displacer element is inits lowermost vertical position, the fluid substantially surrounds thedisplacer element and causes the fluid level to rise so as tosubstantially flll the chamber space between the prism and thedisplacer. Means are provided for moving the displacer element in avertical upward direction in response to an external stimulus so thatthe level of the fluid in the chamber falls to an extent that thechamber space between the prism and the displacer element issubstantially free of fluid and is occupied by a gas, such as air,having a lower index of refraction than either the fluid or the prismmaterial.

By substituting the gas in the space between the prism and the displacerelement for the fluid medium, incident light rays impinging on the frontface of the prism will be totally reflected instead of passing into thefluid and being absorbed by the interior walls of the chamber. A markeddistinction is therefore made by the observer between the two states orconditions of the device.

Another embodiment contemplated by the present invention includes theprovision of a movable float or displacer element having a lightreflecting surface which is partially immersed in an opaque, lightabsorbing fluid. Observation of the reflecting surface is providedthrough a light transparent window. By moving the float, the fluid canbe controlled so as to selectively cover or uncover the reflectingsurface. If the fluid is not interposed between the reflecting surfaceand trans parent window, incident light will be reflected by the surfaceand the visual indication will be bright; however, when the fluid isinterposed between the reflecting surface and the window, the visualindication will be dark..

Therefore, it can be seen that the light modulating device of thepresent invention may be employed to substantially totally reflectimpinging light rays or may be switched to an alternate conditionwherein the light rays are substantially totally absorbed. The devicemay be employed by itself to designate either one of two staticconditions and in such use may be remotely controlled or switched ifdesired. Also, a plurality of devices may be incorporated into a largeviewing screen where each device of the plurality may be individuallyswitched from one condition to another by means of a computer processorso that pictorial or alphanumeric infonnation can be presented to aviewing audience.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present inventionwhich are believed to be novel are set forth with particularity in theappended claims. The present invention, both as to its organization andmanner of operation, together with further objects and advantagesthereof, may best be understood by reference to the followingdescription, taken in connection with the accompanying drawings, inwhich:

FIG. 1 is a perspective diagrammatic view of a typical large screendisplay system incorporating a multiplicity of the novel switchablelight modulating devices of the present invention;

FIG. 2 is a graphic illustration of light ray phenomena on which theconcept of the present invention is based showing a light ray beingreflected and refracted;

FIG. 3 is an enlarged fragmentary view of a portion of the large viewingscreen shown in FIG. 1 and illustrating the front face of a plurality ofswitchable light modulating devices;

FIG. 4 is an enlarged sectional view of a light modulating device orcell as taken in the direction of arrows 4-4 of FIG. 3, with the fluidshown between the prism and displacer element so that it is in the lightabsorbing or dark condition;

FIG. 5 is a plan view, partly in section, of the light modulating deviceshown in FIG. 4 as taken in the direction of arrows 55 thereof;

FIG. 6 is a view similar to that of FIG. 4 illustrating the lightmodulating device switched to its alternate condition for reflectinglight rays;

FIG. 7 is a sectional view of the light modulating device shown in FIG.6 taken in the direction of arrows 77 thereof;

FIG. 8 is a sectionalview of another embodiment of the present inventionemploying a Fresnel-type reflecting surface;

FIG. 9 is a sectional view of still another version of the presentinvention; and

FIG. I0 is a longitudinal sectional view of another embodimentincorporating the present invention utilizing a reflecting surface and alight absorbent fluid to control the visual indication of the device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a largescreen display system is illustrated which includes a computer consoleorprocessor I0 having a cathode ray tube display 11 and a keyboard inputdevice 12 for manually entering data into the memory of the processor.Other ancillary data input equipment may be coupled to the processor 10,if desired. Remotely located from the processor is a large displayscreen 13 adapted to substantially cover a wall for the immediateshowing and viewing of pictorial or alphanumeric information on the facethereof by an audience disposed in an area in front of the screen and asmay be represented by the presence of a plurality of chairs indicated inan audience area 14. The processor 10 is connected to the screen 13 bymeans of a suitable cable 15 so that data information and controlsignals may be transmitted to the screen under the direction of theprogram entered into and stored in V the memory of the processor.

The screen 13 incorporates a multiplicity of light modulating devices orcells in accordance with the present invention as shown in FIG. 3, whichare preferably arranged in a plurality of rows and columns having thefront face of each device constituting the viewing face of the screen.Desired information to be presented on the screen may be readilyachieved by programming the excitation of selected devices in particularrows and columns during a predetermined time cycle so as to operate theselected devices while other nonselected devices will not be operated.In such an instance, the operated plurality of selected devices willform a composite image of the pictorial or alphanumeric informationdesired to be displayed to the audience.

The concept underlying one form of the present invention resides in thebending of light when it passes from one medium having a first index ofrefraction to another medium having a second index of refraction. whichbending is referred to by those skilled in the art as refraction.Refraction of light is caused by the increase or decrease in the speedof light when it enters the new medium and the index of refraction of amaterial is the ratio of the speed of light in air to the speed of lightin that medium. A material with a high index of refraction is said tohave a high optical density." Such a material will, of course, refractlight more than a material with a lower index of refraction. Therefore,according to the laws of refraction, when a ray of light passesobliquely from one medium into another of greater optical density, theray of light is refracted toward the normal (perpendicular). Also,conversely, when a ray of light passes obliquely from one medium intoanother of smaller optical density, it is refracted away from thenormal.

However, if the angle of incidence of a ray of light which is bent awayfrom the normal upon passing from one medium into another of loweroptical density is increased, a condition will be found where therefracted ray just coincides with the surface between the two media. Theangle of incidence at which this occurs is called the critical angle."When a ray of light travelling in a dense medium is incident upon thesurface of a less dense medium at an angle greater than the criticalangle, the ray will not pass through the surface but will be completelyreflected and may be said to undergo "total reflection.

The above laws of refraction are illustrated diagrammatically in FIG. 2,wherein the interface boundary B divides a first region I composed of amaterial having an index of refraction n, from a second region 11composed of a different material having an index of refraction n,, whererr is greater than n,. A light ray L appearing in the first region I isincident at an angle 6 at the boundary and results in a reflected ray R,the observed ray as described herein, and a transmitted ray T. The angleof reflection is, of course, equal to the angle of incidence. The angleof the transmitted rayT is given by:

It will be noted that for (n,/n,) sin 6 1, the angle of the transmittedray T is imaginary so that the incident light is totally reflected.

If the first region I is formed by an o tically transparent materialsuch as glass or lucite (n, and region 11 is formed by the atmosphere orequivalent (n51), then an angle of incidence of, for example, 45, willyield no transmitted ray, and hence substantially total reflection ofthe incident energy. If, however, the second region 11 is filled with aliquid such as water (rr=l .33 the critical angle will be greatlyincreased and so a substantial amount of the energy incident at 45 wouldbe transmitted rather than reflected. If a liquid with an index ofrefraction equal to n is used, transmission would be complete and thereflected energy cut off. The essence of one form of the presentinvention is the controlled movement of a suitable medium in and out ofthe second region 11 so as to switch the behavior of the cell at theinterface between total reflection and, hence, a bright viewing surfaceand essentially total transmission with a consequent dark viewingsurface.

Referring now in detail to FIGS. 4 and 5, one embodiment of the presentinvention is shown which may be referred to as a switchable lightreflector cell" which includes an enclosure 16 having a prism 17 formedin one end thereof having a flat display surface 18 adapted to be viewedby an observer and a wedge-configured rear surface 20 projecting into aclosed chamber 21. The material of the enclosure including the prism 17may be composed of a transparent plastic such as lucite, which serves tototally reflect the incident light ray L at two faces 22 and 23 andredirect it out nonnal to the front face 18 when the cell is switched ONA diverter or displacer element 24 is disposed in the enclosure chamberor hollow housing 21 andis formed with a forward wedge-shaped surface 25corresponding to and adapted to receive the wedge-configured prism rearsurface 20 in substantially fixed spaced-apart relationship so that achamber gap or space is defined immediately behind the prism and infront of the displacer element forward surface. Preferably, theenclosure chamber 21 is suitably dimensioned to accommodate verticalmovement of the displacer element 24 with restriction of lateralmovement effected by the provision of guides 26 formed on opposite sidesof the displacer element which cooperate with the inner wall surfaces ofthe enclosure chambei' 21. The chamber 21 is partially filled with afluid liquid medium 19, having a suitable index of refraction, whichsubstantially surrounds the displacer element 24 except foaa pocket inwhich a gas or gas fluid medium resides and which may take the form ofan air bubble represented by numeral 26 in FIG. 4 that is normally atrest at the top of the chamber 21 between the uppermost chamber wallsurface and the top (not numbered) of the displacer element 24.

Means are provided for moving the displacer element 24 within thechamber 21 which, by way of example, includes a permanent bar magnet 27which is carried on the top of the displacer element 24 and anelectromagnet 28 located on the enclosure 16 so that its pole pieces arecarried thereon and terminate at a suitable distance from the bar magnet27 when the displacer element 24 is resting on the bottom of the chamber21. A wire 30 is coiled about the center section of the electromagnetand is employed for exciting the magnet. The permanent bar magnet 27 hasa north poleN and a south pole S.

When the electromagnet 28 is excited by passing a current through thecoil 30 so that a south pole appears above the north pole N on themagnet 27 and a north pole of the electromagnet is above the bar magnetsouth pole S, the displacer element 24 will be lifted vertically towardthe terminating end of the pole pieces of the electromagnet 28, and,because of the magnetic field of the permanent magnet 27, the displacerelement 24 will remain in its raised position after the excitationcurrent has been removed. As shown in FIG. 6, the electromagnet 28 ispreferably supported in the top wall of enclosure 16 such that it is notcontacted by the permanent magnet 27 in the raised position of thedisplacer element 24. The displacer element 24 in the raised position isillustrated in FIGS. 6 and 7 wherein the displacer element 24 is raisedso that the fluid medium 19 flows under this displacer element 24, andthe gas pocket or air bubble 26 divides and moves to the sides of thechamber including occupying the space between the rear surface 20 of theprism 17 and the forward surface 25 of the displacer element 24 so as topermit total reflection of the light and a bright output as illustratedin FIG. 7 by the reflected light ray R.

However, a momentary excitation of the electromagnet 28 such that anorth pole appears near the north pole N of the bar magnet 27 carried bythe displacer element 24 and an electromagnetic south pole appears nearthe south pole S of the displacer element magnet 27 will cause thedisplacer element 24 to be repelled and therefore to resume its originalposition against the bottom of the chamber 21. The fluid medium 19 isthen displaced upwardly to a point where the space or gap between theprism surface 20 and the displacer element 24 is again filled by thefluid medium 19 and transmission into the second region reestablished,resulting in a dark display output.

In other words, when the displacer element 24 is in its lowermostposition, the level of the fluid rises in the chamber to an extentcausing the fluid to contact substantially the entirety of the rearsurface of the prism. On the other hand, when the displacer element 24is pulled up and held in its uppermost position, the fluid level drops.The rear surface of the prism 20 then interfaces with gas, air, oranother low refractive index substance used to fill the chamber incombination with the fluid. Thus the displacer element 24 in lowermostposition displaces the liquid from the lower portion of the enclosedchamber 21 to a position where it inhibits light reflection.

In accordance with the present invention, the contrast ratio between theconditions of light and dark display is maximized by selecting the fluidmedium 19 from a class of transparent, low viscosity liquids having anindex of refraction substantially equal to that of the prism materialand exhibiting good wetting characteristics in respect of the materialof which the prism is comprised. Further, the surface of the displacerelement adjacent the window should be as light absorptive as possible.If

the liquid has an index of refraction greater than that of the prismmaterial, some internal reflections can take place and, depending uponthe reflectivity of the displacer surface adjacent the prism, theaforesaid contrast ratio will be reduced. A highly satisfactory contrastratio may be realized by making the prism of transparent plastic, ofsuitable index of refraction, such as Lucite (Trademark of E. I. du Pontde Nemours 8r. Co.). The displacer element may be of various materialswith a suitable black surface, for example, black plastic materials suchas Bakelite or black loaded polystyrene. The fluid may be water or otherliquid of suitable characteristics, such as Brayco 900 Dry CleaningSolvent DD680(2) Type l Batch B6LTl manufactured by the Bray Oil Companyof Los Angeles and Richmond, California.

It is further contemplated by the present invention that the fluid mediafilling the chamber may be two liquids rather than a liquid and a gassuch as air. In this case, the fluid replacing the gas should be atransparent liquid having an index of refraction lower than that of theprism and a density substantially different from that of the otherliquid so that the two liquids do not mix.

It is within the concept of the present invention to provide that thecells or devices described above can be fabricated such that one-turnelectromagnets will suffice for the switching operation and there willbe sufficient unifonnity to assure reliable operation with normalelectrical full signal pulses and no operation with half-amplitudesignal pulses. This will make possible coincident current operationwherein a two-dimensional grid is used to link a number of cells and agiven cell switched by the application of half-amplitude pulses to thetwo lines common to the desired cell. This is illustrated by theexcitation lines 1, 1' of FIG. 3. Also, it is anticipated thatassemblages of cells of the type described herein can be linked byswitching lines defining alphanumeric characters and that excitation ofa given character line will result in all cells associated with thecharacter to be displayed being turned ON. In other instances, it isanticipated that all cells in a given assembly would be linked by acommon turnoff line so that one signal can be employed to erase acomplete display.

The device or cell described with respect to FIGS. 4 and 5 provides asharply defined reflecting angle because of the large front-to-backdepth of the prism. This situation can be readily improved using areflecting surface made in the form ofa Fresnel lens such as is shown inFIG. 8 represented by numeral 31. In this instance, the individualreflecting surfaces are small and shallow, but the assemblage ofreflecting surfaces yields a total reflection with a potentially wideviewing angle. A displacer element 32 is included which provides a flatforward face 33 which is immediately behind the assemblage of reflectingsurfaces of the prism so as to define a space or gap 34 which isalternately occupied by a fluid medium or a gas pocket or bubble similarto the fluid medium and gas pocket or bubble arrangement shown withrespect to the embodiments of FIGS. 4 and 5. The displacer element 32includes guide members at their'respective corners, such as arerepresented by numeral 35, which slidably bear against a rearmost wall36 of a chamber 37 in which the displacer element 32 vertically movesand the rearwardly facing opposite wall of the chamber 37 immediatelybehind the prism 31. Construction in this fashion permits the displacerelement to move vertically with restrictive lateral and longitudinalmovement. Bar magnet 38 is carried by the displacer element, and anelectromagnet is employed in a similar fashion as previously described.

With respect to the embodiments shown in FIGS. 4 and 8, under somecircumstances, such as for ON/OFF indicators, it may be desirable tohave a controllable or switchable reflector cell that is bright onlywhen the electromagnet is excited, going dark when the excitation isremoved. This can be readily achieved by preventing physical contact ofthe magnet and the electromagnet so that the residual attracting forceis not too strong. When excitation is removed, gravity will then causethe displacer element to drop and thus turn off the cell.

ment. Excitation of the two electromagnets would be such as 1 to produceopposite polarities near the displacer magnet. During element switching,one electromagnet would then be attracting and the other repelling sothat the magnet would be positively held by one or the other of theelectromagnets, making it less likely to change state because ofmechanical vibration. Also, it is to be understood that the displacerelement may be replaced by magnetic particles suitably suspended in thefluid medium. An electromagnet close to the reflecting surface wouldthen hold the fluid medium against the face, turning the cell OF F," anda second electromagnet. away from the face, would serve to hold thefluid medium away, thus leaving the cell ON.

Bistable fluid amplifiers may also be useful in actuating thecontrollable or switchable light reflecting cell of the presentinvention. Such an implementation is illustrated in FIG. 9. A cellenclosure 40 is provided having an input port 41 and an output port 42disposed at opposite ends thereof and further including a lens or prism43 having a display face 44. A chamber 45 is formed within the cell 40and is in fluid communication at its opposite ends with the input andoutput ports so that a pressurized fluid stream may be introducedthrough the input port 41, flow through the chamber 45, and dischargethrough the output port 42. Situated within the chamber 45 and extendingacross the chamber midway between its opposite wall surfaces is a vane46 shaped in cross section so that a narrow angled end faces the inputport 41, while a thickened second opposite end faces the output port 42.The vane 46 di vides chamber 45 into discrete passageways 47 which liebetween one surface of the vane 46 and the rearmost surface of the prism43 and a second chamber 48 which lies between the other surface of thevane 46 and the rearmost wall surface of the chamber 45. Therefore,fluid entering at the inlet port 41 can be directed into eitherpassageway 47, where it turns the cell OFF" by allowing light to betransmitted into the fluid or into passageway 48, leaving the cellhighly reflecting and hence ON." A movable deflector 50 may be rotatablymounted in the inlet port 41 so as to deflect the input fluid mediumstream into passageway 47 or the chamber 48. Bernoulli forces maintainthe fluid on one side or the other of the vane 46 until a deliberateforce is applied to the fluid medium to redirect it. The switching forcemay take the form of transverse fluid jets near the inlet port 41, ifdesired, that serve to momentarily deflect the stream, or,alternatively, if the fluid carries magnetic particles, it may bemomentarily deflected using appropriately placed electromagnets.

Therefore, it can be seen that the embodiments of the present inventionas shown in FIGS. 4, 8, and 9 employ a boundary area between two mediawherein light incident on the boundary from the first medium can beeither substantially totally reflected or transmitted into the secondmedium where selection between the states is made through movement of afluid into or away from the boundary region through the use ofdeliberately applied control signals or stimuli. Devices or cells may beused individually to display the ON/OFF state of a circuit or condition,or a plurality of cells may be placed together in a mosaic such as for alarge display screen for displaying pictorial infonnation oralphanumeric characters.

Another embodiment incorporating the present invention is illustrated inFIG. 10, wherein the light modulating device includes an enclosurehaving end and sidewalls defining a cavity 61 for holding a quantity oflight absorbent or opaque fluid 62 such as india ink, for example. End63 of the enclosure is composed of light transparent materialconstituting a transparent window for receiving impinging incident lightrays indicated by reference character L and for transmitting reflectedor observed light as indicated by reference character R.

A displacer element 64 is movable disposed in the cavity 61 having areflecting surface 65 carried on its end adjacent the window 63, butspaced therefrom to provide a gap 66. The displacer element iscontrollably moved between alternate positions within the cavity todisplace the fluid into or out of the gap 66. The reflecting surface maytake the form of a flat mirror or the form of a multiple wedgeddispersive reflector, as illustrated. Means, including an electromagnet67 and a permanent magnet 68 carried on the element, are employed tocontrol the movement and hence the position of the displacer element.

When the electromagnet 67 is not energized, the displacer element 64will be forced by gravity to settle into the fluid 62, causing a portionof the fluid to occupy the gap 66. Thus, incident light will be absorbedby the fluid and the visual indication at the window 63 will be dark.However, when the electromagnet 67 is energized, such as is thecondition illustrated in FIG. 10, attraction takes place in cooperationwith magnet 68, which causes the displacer element 64 to besubstantially out of the fluid. In this latter event, the fluid leavesthe gap 66, and incident light rays reach the reflecting surface 65 andare reflected outwardly through the window 63 as bright observed light.

Therefore, it can be seen that the light modulating device iscontrollably switched between alternate conditions of dark and brightvisual indications. The gap 66 provides a changeable interface boundarythat is readily switched by the electromagnetic control means to providethe desired visual indication.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects, and therefore the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of this invention.

lclaim:

l. A reflective light modulating device for switching incident lightapplied thereto between visually observable states of high lightreflection and of light absorption, comprising:

a hollow housing having one'portion thereof formed into a lighttransparent prism having a predetermined index of refraction;

a fluid having a predetermined index of refraction substan- 10 and outof contact with said prism to modify the visually observable states ofthe device. 2. The invention as defined in claim 1 wherein said movingmeans includes a permanent magnet carried by said diverter means and anelectromagnet carried on said housing for producing an electromagneticfield sufficient to move said diverter means.

3. The invention as defined in claim 1 wherein said gas pocketconstitutes a quantity of air captured within said housing and beingsubstantially buoyant with respect to said fluid.

4. The invention as defined in claim 2 wherein a rear wall of said prismand a forward wall of said diverter means are spaced apart so as todefine a gap therebetween constituting a controllable light reflectingboundary adapted to be occupied alternately by said fluid and said gaspocket in response to movement of said diverter means.

5. The invention as defined in claim 2 wherein said prism rear walltakes the form of a wedge lens projecting into the hollow of saidhousing and said diverter means forward wall is formed in shape tocorrend to said wedge lens.

6. The invention as de med in claim 4 wherein said prism rear wallconstitutes a Fresnel lens and said diverter means forward wall takesthe form of a flat surface.

7. The invention as defined in claim 4 wherein said prism rear wallconstitutes a light difiusing and reflecting surface.

8. The invention as defined in claim 4 including guiding meanscooperatingly disposed between said diverter means and said housing soas to maintain said gap during movement of said diverter means.

9. The invention as defined in claim 1 wherein said moving 4 meansincludes electromagnetic means and further includes signal pulsing meanscoupled to said electromagnetic means adapted to remotely produce signalpulses sufiicient to selectively excite said electromagnetic means tomove said diverter means in response to the presence of anelectromagnetic field.

tially equal to or greater than the index of refraction of

1. A reflective light modulating device for switching incident lightapplied thereto between visually observable states of high lightreflection and of light absorption, comprising: a hollow housing havingone portion thereof formed into a light transparent prism having apredetermined index of refraction; a fluid having a predetermined indexof refraction substantially equal to or greater than the index ofrefraction of said prism adapted to substantially occupy the hollow ofsaid housing except for the presence of a gas pocket formed in saidfluid having a different index of refraction than said fluid; divertermeans movably disposed within said housing and being substantiallyimmersed in said fluid; and means cooperatively coupled to said divertermeans for controllably moving said diverter means so as to selectivelyalternately locate said fluid and said gas pocket into and out ofcontact with said prism to modify the visually observable states of thedevice.
 2. The invention as defined in claim 1 wherein said moving meansincludes a permanent magnet carried by said diverter means and anelectromagnet carried on said housing for producing an electromagneticfield sufficient to move said diverter means.
 3. The invention asdefined in claim 1 wherein said gas pocket constitutes a quantity of aircaptured within said housing and being substantially buoyant withrespect to said fluid.
 4. The invention as defined in claim 2 wherein arear wall of said prism and a forward wall of said diverter means arespaced apart so as to define a gap therebetween constituting acontrollable light reflecting boundary adapted to be occupiedalternately by said fluid and said gas pocket in response to movement ofsaid diverter means.
 5. The invention as defined in claim 2 wherein saidprism rear wall takes the form of a wedge lens projecting into thehollow of said housing and said diverter means forward wall is formed inshape to correspond to said wedge lens.
 6. The invention as defined inclaim 4 wherein said prism rear wall constitutes a Fresnel lens and saiddiverter means forward wall takes the form of a flat surface.
 7. Theinvention as defined in claim 4 wherein said prism rear wall constitutesa light diffusing and reflecting surface.
 8. The invention as defined inclaim 4 including guiding means cooperatingly disposed between saiddiverter means and said housing so as to maintain said gap duringmovement of said diverter means.
 9. The invention as defined in claim 1wherein said moving means includes electromagnetic means and furtherincludes signal pulsing means coupled to said electromagnetic meansadapted to remotely produce signal pulses sufficient to selectivelyexcite said electromagnetic means to move said diverter mEans inresponse to the presence of an electromagnetic field.